MERCURY CONTAMINATION

Mercury Contamination in the Aquatic Ecosystems

Abstract

Sources of mercury contamination in aquatic systems were studied in a comprehensive literature review. The results show that the most important anthropogenic sources of mercury pollution in aquatic systems are: (1) atmospheric deposition, (2) erosion, (3) urban discharges, (4) agricultural materials, (5) mining, and (6) combustion and industrial discharges. Capping and dredging are two possible remedial approaches to mercury contamination in aquatic systems, and natural attenuation is a passive decontamination alternative. Capping seems to be an economical and effective remedial approach to mercury-contaminated aquatic systems. Dredging is an expensive remedial approach. However, for heavily polluted systems, dredging may be more effective. Natural attenuation, involving little or no cost, is a possible and very economical choice for less contaminated sites. Proper risk assessment is necessary to evaluate the effectiveness of remedial and passive decontamination methods as well as their potential adverse environmental effects. Modeling tools have a bright future in the remediation and passive decontamination of mercury contamination in aquatic systems. Existing mercury transport and transformation models were reviewed and compared.

Table of Contents

Abstract2

Table of Contents3

Introduction4

Sources of contamination5

Atmospheric deposition7

Erosion sources8

Urban sources9

Agricultural sources10

Mining sources11

Combustion and industrial sources11

Remediation and passive decontamination for mercury pollution12

Dredging13

Conclusion15

Bibliography17

Mercury Contamination in the Aquatic Ecosystems

Introduction

Mercury is a hazardous environmental contaminant. In Japan, 2252 people have been affected and 1043 have died due to Minamata Disease for the past two decades, caused by elevated mercury pollution from a chemical plant (Kudo and Miyahara, 1991). Toxicology studies also proved that mercury, especially methyl mercury (MeHg), is very toxic to the human embryo and fetus ( Bakir et al., 1973; Amin-Zaki et al., 1976 and Harada, 1995). MeHg is the most toxic form of mercury. In aquatic systems, bioaccumulation through food chain may cause high levels of mercury contamination in fish from even very low concentrations of MeHg in water.

In aquatic systems, mercury exists in elemental, inorganic, and organic forms. Elemental mercury (Hg0) is the only metal in liquid form at room temperature. It has high volatility and relatively low water solubility (Lindqvist and Rodlhe, 1985). Aqueous inorganic mercury has two valences, +1 and +2. Mercury with valence +2 is more widely spread in the environment ( Loux, 1998). In most mercury studies, HgII is used as a substitute for inorganic mercury. HgII consists of both Hg2+ free ions and Hg2+ complexes. Chloride, hydroxide, sulfide, dissolved organic matter (DOM), and other chemicals are found in Hg2+ complexes (Morel et al., 1998). Aqueous organic mercury may be placed in two categories: (1) covalently-bonded organomercurials, such as MeHg and dimethyl mercury (dimethyl mercury being less important than MeHg in mercury transport and transformation), and (2) mercuric complexes with organic matter, such as humic substances (Gill and Bruland, 1990). Mercury can either be dissolved or remain in a particulate state in aquatic systems. It is believed that suspended organic matter plays an important role in whether mercury is dissolved or remains in a particulate state ( Meili, 1997).

In the Mercury Study Report to Congress (USEPA, 1997), sources ...